Vehicles may be configured with a hybrid propulsion system that utilizes at least two different sources of torque for propelling the vehicle. As one non-limiting example, a hybrid propulsion system for a vehicle may be configured as a hybrid electric vehicle (HEV), wherein an electric motor and an internal combustion engine may be selectively operated to provide the requested propulsive effort. Similarly, during deceleration of the vehicle, the electric motor and engine can be selectively operated to provide vehicle driveline braking in order to recapture kinetic energy of the vehicle. For example, as described by U.S. Pat. No. 6,890,283, one of two motors of the vehicle may be operated to provide driveline braking torque for a vehicle. In this way, vehicle efficiency may be increased.
The inventors of the present disclosure have recognized disadvantages with the above approach. As one example, the motor may be damaged during some braking events due to overheating. As another example, the motor may not be operating in an efficient operating state when providing driveline braking torque. Thus, energy may not be effectively recaptured where the motor is operated in an inefficient manner or the motor may be damaged if braking is performed at some operating conditions.
As another approach, the inventors herein have provided a hybrid propulsion system for a vehicle, comprising at least one drive wheel; a first motor coupled to the drive wheel, said first motor configured to selectively generate electrical energy from kinetic energy received at the drive wheel; a second motor configured to selectively generate electrical energy from kinetic energy received at the drive wheel; a transmission including a first end coupled to the first motor and a second end coupled to the second motor; and a control system configured to vary a level of electrical energy generated by the first motor relative to the second motor in response to a thermal condition of at least one of said first and second motors to provide vehicle braking. In this way, a first motor and a second motor may be coordinated to provide sufficient vehicle braking, while reducing motor operation at thermal conditions where the motor may be damaged.
As yet another approach described herein, a method of operating a hybrid propulsion system for a vehicle is provided. The hybrid propulsion system includes a first motor coupled to a drive wheel and a vehicle braking device coupled to the drive wheel via a transmission. The method comprises receiving a vehicle braking request from a user at a user input device; in response to said vehicle braking request, adjusting a level of vehicle braking provided by the first motor based on an amount of electrical energy generated by the first motor at said level of vehicle braking provide by the first motor; and adjusting a level of vehicle braking provided by the vehicle braking device based on said level of vehicle braking provided by the first motor. In this way, a first motor and a second motor may be coordinated to provide sufficient vehicle braking, while improving the efficiency at which the energy is recaptured by the hybrid vehicle during a braking operation.
It should be appreciated that the various concepts that have been provided in the Background and Summary are non-limiting examples and that these and other approaches will be described in the Detailed Description in greater detail. Additionally, the various approaches described herein and the claimed subject matter are not necessarily limited to addressing the above mentioned issues.